President Volodymyr Zelenskyy said that Ukraine's formal candidature to join the European Union was a big step towards strengthening Europe at a time when Russia was testing its freedom and unity.
Friday marks the fourth month since Russian President Vladimir Putin sent troops across the border into Ukraine, sparking the biggest conflict in Europe since World War Two.
Authorities in the town of Derhachi, northwest of Kharkiv, said heavy Russian shelling had knocked out most of the electrical and natural gas supply.
Ukrainian troops may have to retreat from the eastern frontline city of Lysychansk to avoid encirclement, regional governor Serhiy Gaidai said on Thursday.
Ukraine said its troops were still holding out in Sievieorodonetsk, across the river.
Three cruise missiles hit the port city of Mykolaiv in Ukraine's south, while two more were shot down near Odesa, the Ukrainian armed forces said.
Russia said it had struck Ukrainian army fuel tanks and military equipment near Mykolaiv with high-precision weapons, Interfax reported.
Reuters was unable to independently verify the situation on the ground.
Ukraine received US supplies of powerful HIMARS long-range weapon systems.
The United States will provide additional $450 million in security assistance to Ukraine, including more long-range rocket systems, US officials said on Thursday.
The EU leaders accepted Ukraine as a candidate to join the bloc on Thursday.
The EU should stop adding sanctions on Russia and instead push for a ceasefire and the start of negotiations, a senior aide to Hungarian Prime Minister Viktor Orban said on Thursday.
Prime Minister Boris Johnson said Britain would be willing to help with demining off Ukraine's coast and may offer insurance for ships to help with grain exports.
The G 7 rich democracies will try to show long-term support for Ukraine at a summit starting on Sunday.
Turkey said it was looking into claims that Ukrainian grain had been stolen by Russia and shipped to countries including Turkey, although no stolen shipments had been found so far. Russia has denied theft allegations.
In 2022, Ukraine could harvest more than 52 million tons of grain, according to analyst APK-Inform.
A dozen EU countries have been affected by cuts to Russia's gas supply, according to the bloc's climate policy chief, amid a deepening energy standoff with Moscow.
Ukraine held a preliminary hearing on Thursday in its first trial of a Russian soldier charged with raping a Ukrainian woman during Russia's invasion, the first of what prosecutors say could be dozens of such cases.
Zelenskiy wrote on Twitter that Ukraine's future is in the EU.
Ukraine will prevail. Today marks the beginning of a long journey that we will walk together, said Josep Borrell, EU foreign policy chief.